wcpa annual concrete pavement workshop principles … · aasho road test wcpa annual ... quality...

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Principles of Quality Management and Statistical Specifications

Dennis DvorakFHWA Resource Center

WCPA Annual Concrete Pavement Workshop

Dennis Dvorhak Presentation February 13, 2015 1 of 62

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Topics Why QA? Variability Six building blocks of a Quality Assurance program QC plan Why PWL Purpose of incentives



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Why QA?

Change in Agency Demographic Agency Personnel Levels Change in Contractor Demographic Rational Assessment of Pay Reduction in Product Variability



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AASHO Road Test



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Construction 1956 to 1958 Highly controlled Specifications based on prevailing state practices Found that variabilitycould not be eliminated



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Sources of Variability

Material Process Sampling Testing

CompositeVariability



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Six Building Blocks Agency Acceptance (QV) Contractor Quality Control (QC/Process Control) Independent Assurance Dispute Resolution Qualified Laboratories Qualified Personnel



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Independent Assurance Assessment of personnel proficiency and equipment Provides independent check on reliability of results of both partners Uses Split sample Not used to make a determination of quality/acceptability of the product



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Sources of Variability

Material Process Sampling Testing

CompositeVariability



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Dispute Resolution Formal system designed to address significant differences between partners data of such magnitude to impact payment Not intended to address day to day issues Required (by FHWA) when contractor results used in acceptance decision Generally uses a “referee” lab



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Qualified Laboratories & Accredited Laboratories

State central labs must be accredited. Private labs conducting dispute or Independent Assurance testing must also be accredited. All other labs must be qualified through a state sponsored program.



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Requirements for Personnel Qualification/Certification

Recommended program guidelines:• Formal training; hands‐on training • On‐the‐job training • Written and performance examinations• Periodic re‐qualification (typically 2‐5 years)• Process to remove personnel performing procedures incorrectly, falsifying statements or data



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Testing Variability Inherent in the procedures and apparatus

Influenced by the technicians



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Testing VariabilityProcedure 95% Lower Limit Test Result 95% Upper Limit

Sieve analysis (% passing ½”) 24% 28% 32%

Slump 2” 2 ½” 3”

Air content 4.9% 5.5% 6.1%

Rodded unit weight for aggregate

114.5 lb/ft3 120 lb/ft3 125.5 lb/ft3

Compressive strength 3,390 lb/in2 3,600 lb/in2 3,810 lb/in2

Flexural strength 602 lb/in2 700 lb/in2 798 lb/in2



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Six Building Blocks (23 CFR 637) Agency Acceptance‐PWL motivates minimizing all variability Contractor Quality Control‐Material and Process Independent Assurance‐Sampling and Testing Dispute Resolution‐Sampling and Testing Qualified Laboratories‐Testing Qualified Personnel‐Sampling and Testing



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Random Sampling(23 CFR 637.205(e)) All samples used in the acceptance decision shall be random samples• All materials will have an equal probability of being sampled

• Removes bias• Reduces potential for fraud

The tests on the first load in the morning are not random!



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Random Sampling

Simple Random Sampling

LOTLOT



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Stratified Random Sampling

Stratified Random Sampling

Sublot1

Sublot2

Sublot3

Sublot4

Sublot5

LOT



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Non‐Random Sampling Used at start‐up or when process adjustments are made• Example: adjusted air entrainment admixture dosage

• Sample immediately and repeat testing to monitor the adjustment

• Return to random sampling when desired results are consistent

• What should the agency do?



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Boston Central Artery/Tunnel Project



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Quality Control Defined

Quality Control ‐ The system used by a Contractor to monitor, assess, and adjust their production and placement processes to ensure that the final product will meet the specified level of quality.



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Quality Control Uses real time feedback A good QC system:

• Doesn’t try to accommodate Agency requirements

• Implements QC procedures as standard practice

• Isn’t just paperwork…it’s a mindset



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Quality Control

Integrated throughout the organization Not just responsibility of QC personnel Quality can only be achieved by skilled and properly trained frontline workers

Comprehensive, systematic, and continuous approach Proactive, not reactive Focus on preventing problems not finding them Zero Defects philosophy



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Scope of Quality Control Activities Contractor’s QC system should address:

• Materials production • Materials transportation and handling• Field placement procedures• Calibration and maintenance of equipment• Sampling, testing, and inspection to maintain each process “in control”

• Use of QC information to make timely adjustments



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Scope of Quality Control Activities

Inspection is as important to Contractor QC as sampling and testing Necessary to minimize visually detectable problems



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Project Quality Control Organization

No “one‐size fits all” QC organization structure Will vary depending on the size and complexity of the project



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QC Plan A project specific document prepared by the contractor which identifies QC procedures that will be used to maintain production and placement processes in control and meet the agency specification requirements.



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Poor Example Contractor’s QC plan states:

• “Materials, equipment and methods used to construct concrete pavement will conform to Section 501 of the specifications”

• “Quality control testing will be performed in accordance with Section 501.14 of the specifications”

Module 6 ‐ 6



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Improved Example Contractor’s QC plan states:

• Smoothnesso 20’ straightedge advanced at 10’ increments

o Paving foreman will maintain a log of all “events” indexed by station

o Smoothness test results will be provided to the paving foreman for analysis and approval within one hour of testing

Module 6 ‐ 7



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Setting Expectations



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Quality Control Plan Materials production processes Materials transportation and handling Field placement procedures Calibration and maintenance of equipment Activities (sampling, testing and inspection) to maintain each process in control Means to make timely adjustments and corrections



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QC Plan Format and Contents Agency specifications normally identify minimum QC Plan requirements Project specific and reflect actual QC processes that will be applied Written in straightforward and plain speaking manner Comprehensive in the amount of information provided



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Visual Inspection for Quality Control

Visual inspection is also essential to achieving quality Observations and measurement of

• Equipment• Environmental conditions• Materials• Workmanship

Prevention based, not detection based



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QC Inspection of Equipment Ensure that all equipment is in good working condition and is properly maintained Periodic calibration of equipment should also be performed Document prior to production



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QC Inspection of Environmental Conditions

Monitoring and measurements to ensure that the proper physical environment is being provided for:• Storage• Production• Placement• Curing of individual materials or products



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Inspection by Production Personnel Contractor’s should strive to create a “Quality Culture” throughout the company Personnel are aware of how their actions can affect the quality of the product Contractors must invest in the continual education and training of their work force in order to maximize their involvement in Quality Control



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Inspection by Production Personnel

Skilled Laborers and Foremen should be capable of identifying unacceptable materials prior to incorporation in the Work• Should take initial responsibility for accepting or rejecting it

• Should always communicate their findings and proposed actions with their QC Inspectors



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July 2006 motorist fatality Partial collapse of tunnel ceiling on I‐90



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Agency Monitoring QC Activities

Periodic visual observation of QCinspection, sampling, and testing Review of QC records/documents Provide feedback to contractor’spersonnel



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Maine Example Data analysis of materials testing from 1978‐1998 Per cent “passing” tests ranged from 87%‐92% every year Confirms that our industry, without incentives, operates around 90 PWL



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Normal Distribution Previous example provides a picture of variability Pattern formed is referred to as Normal Distribution Properly obtained statistical sample for an entire lot of most construction material will form aNormal Distribution Curve



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This Empirical Rule states that:

–1Sn 1Sn 2Sn–2Sn 3Sn–3Sn

6895.599.7

x

68 – 95 – 99.7 Rule

68% of all possible samples are clustered about the mean within ± 1 standard deviation

95.5% are within ± 2 standard deviations

99.7% are within ± 3 standard deviations



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Testing Targets and LimitsBased on Normal Distribution

Specifications normally identify targets and/or limits for individual quality characteristics

Specification limits should be based on the principle of normal distribution

6.55.5 7.05.0 8.07.56.0Lower Spec

LimitUpper Spec

LimitTarget

Air Content (%)



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Standard Deviation

Sample standard deviation (s)

s =∑(Xi - X)2

n - 1



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PWL Using the sample data, with its mean and standard deviation, we can determine the quality level of the sample



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PWL Estimates the percentage of material within

specification limits• Assumes normal distribution

1.0or 100%



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PWL Efficiently captures mean and standard

deviation in one quality measure

X 3s2s1s-3s -2s -1s

X - means - standard deviation



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Single Specification PWL

USL

LSL

PWLL

PWLUorX

X



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Double Specification PWL

- 100 =PWLL

LSLUSL

PWLU

X

USL

LSL

PWL

+



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Estimating PWL in Four Steps1. Obtain random samples2. Compute

• Mean ( x ) • Standard deviation (s)

3. Compute quality index (Q)4. Convert Q to “estimated” PWL



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3s2ss-3s -2s -s

Compute Q

QL =X – LSL

s

USL - X

sQU =

LSL

USL

X

QL QU



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QL → PWLL

Convert Q to PWL Lookup estimated PWL from Q for a specified

number of samples (n)

X3s2s1s-3s -2s -1s

PWLL

LSL



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Question

Why would you pay more than 100% for a pavement product?

3% Incentive Cost less than 1 year (3% of 30 year pavement design life) Gain: How much longer will it last?

• Better Mixture => Less cracking / reduce early deterioration risk• Smoother ride => less dynamic loading



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What Are You Paying For? Specifications are set at a level for average work

• Average contractor• Increases competition

Low bid system• Won’t get better than that• Do the work the cheapest at the minimum level

Not paying for higher quality

Ford Focus

You get what you pay for!



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Want Higher Quality? Higher quantity costs money

• Benefit of longer life pavement exceeds the initial cost => economic decision

• Better materialo Water reducer that won’t give problems in hot weathero Cost of a larger stockpile for a third aggregateo Cost of a third conveyer and possibly a third aggregate bin

• More personnelo Additional QC testingo Additional QC personnel

• Newer equipment



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How? Quality contractor has control of the process

• Less variability• Less chance of rework

Incentives pay for the extra costs of higher quality Incentives give the bidding advantage to the better contractor• They know they can meet the incentive requirements• They can reduce the bid price by some portion of the incentive



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Why? Higher overall quality with a limited number of incentives• Quality contractor has the quality mindset• Quality contractor applies better process control to all work

• A few incentives provide capital to do all things better Reduces inspection time and cost

• No time spent on disincentives• No time spent on rework

Reduce delays due to rework• Open to the public sooner



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Pay Factor Formula A pay factor formula presents a mathematical equation that typically derives a linear schedule of pay from the PWL AASHTO provides a recommended equation:

Pay Factor (PF) = 0.55 + 0.5 (PWL)(PWL is expressed as a decimal value in this equation)



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Pay Factors Currently many states have pay factors for:

• Strength• Thickness

Future???



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Incentives Incentives and disincentives should be related to performance• Another State ‐ 10‐20% reduction in pay for small deviation from specification

Non‐conforming materials• Strength• Thickness• Air content



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